30. Mammalian development Flashcards
What is considered day 0?
Fertilisation
What happens at day 1?
First cleavage
What happens at day 2?
2 cell stage then 4 cell stage
What happens from days 3-4?
8 cell stage
What happens at day 4?
Compacted morula
What is formed at day 5?
Early blastocyte
What is formed at day 6-7?
Late stage blastocyte (hatching)
What happens at day 8-9?
Implantation of the blastocyte
Why is there no yolk in mammal eggs?
Because all the nutrients the embryo requires are provided by the mother
What does the first cleavage produce?
Produces blastomeres that are developmentally equivalent (holoblastic cleavage)
What directions are the first and second cleavage?
First cleavage is a vertical cleavage
Second cleavage is one vertical and one horizontal
Why do cells become smaller with each division?
For the restoration of the nuclear to cytoplasm ratio
What happens with the activation of the embryo genome?
- Destruction of pre-stored mRNA
- But pre-stored proteins may continue to function and regulate development for some time
What is cadherin?
A calcium dependent cell adhesion molecule
What does cadherin do?
Mediates adhesion between blastomeres
- Cell outlines coalesce to form a morula
What does the cleavage of blastomeres result in?
Some cells enclosed within the inner compartment of the morula
What is cavitation?
What fluid begins to accumulate between blastomeres
What does cavitation result in the formation of?
A blastocoel
What is the outer layer of cells in the blastomeres?
The trophoblast/trophectoderm
What does the trophectoderm give rise to?
The placenta
What are the inner cells of the blastulation known as?
The inner cell mass
What does the inner cell mass give rise to?
The embryo
What is the purpose of the zona?
- The zona prevents cell-cell contact of the embryo and the oviduct wall so that there is no premature hatching
- Premature hatching causes a tubal pregnancy
What happens during zona hatching?
- Hatching occurs in the uterus just before implantation
- Blastocyst secretes proteases that weaken the zona so that it implants to the uterine epithelium
What are the changes in physiology of the embryo during the preimplantation period?
Embryo switches to using glucose rather than pyruvate
How does the zygote generate energy?
Generates energy from low levels of oxidation of pyruvate and/or lactate with aspartate (and other amino acids).
What does the blastocysts generate energy from?
Both aerobic glycolysis and the oxidation of glucose
What is the morula defined as?
Once an embryo has compacted and formed tight junctions between blastomeres, the embryos is known as a morula
How is the zona digested during zona hatching?
- Apical proteases (and uterine proteases) digest the glycoprotein zona pellucida
- The hatched blastocyst is free to implant into the endometrium of the uterus
What does Na/K ATPase activity on the basolateral membrane result in?
An ionic gradient is formed and water flows into the embryo through aquaporins
What are the exchanges during Na/K ATPase activity?
3 Na go in and 2K go out, water goes in
What are the three phases of implantation?
Apposition, attachment and invasion
What happens in the attachment phase?
- Loss of zona and glycocalyx
- Vascular changes
What cells directly contact the uterus during attachment?
- Trophoblast directly contacts uterine epithelium
- Trophoblast cells start to penetrate epithelium
What happens after the adhesion phase of embryo implantation?
- Trophoblast cells penetrate uterine epithelium, decidua and up to a third of myometrium
- Target maternal blood vessels and degrade them to provide adequate blood supply to growing foetus and placenta
